The Motherboard: The motherboard is where it all comes together. Make sure you get a board that supports the components you wish to add. For example, make sure it supports the processor, video card and hard drives you wish to use. Some extras to look for include serial ATA ports, a PCI Express slot, a firewire port and support for USB 2.0. In addition, make sure the board correctly supports separate front and rear USB ports on separate controllers. Look for on-board Ethernet and modem jacks so you won't need to add pci cards for them. Be sure there are enough slots for future memory expansion.

The Processor: Processors from either AMD or Intel will provide excellent processing power for your system. Match the type of processor up with the motherboard you choose. If you plan to do a lot of hard core gaming or video editing, buy the highest level you can afford. For most everyday tasks, you can often save a bit by buying something that has been out for a few months.

Processor Cooling Fan/Heat Sink: This often comes with your processor, but you'll need one if it doesn't. Consider liquid cooling if you plan to overclock your system.

The Case: Look for a model that opens easily, provides easy to remove and replace back slot covers and plenty of drive bays. If it includes a power supply, be sure it is rated for 400 Watts or higher. Make sure the case offers front USB ports if your motherboard has connections for them.

Power Supply: If this doesn't come with your case, look for a model rated for a minimum of 400 Watts. This is one area where price often reflects quality. Better units will actually offer sustained power at their rated wattage rather than just maximum levels. Be sure the power supply can handle all those system components powering up at startup.

Cooling Fans: In addition to fans in the power supply, processor and graphics card, you'll want to consider additional case-mounted fans. One to pull air in and another to push air out should be adequate. Mount one at the front for the case and the other at the rear for best circulation. Drawing more air in than you exhaust will help prevent dust from being pulled into air vents since air will be forced out of them.

Memory: For WIndows Vista, choose at least 1GB of memory. If you wish to use your system for gaming or video editing, install 2-3GB. Your system probably won't benefit from adding much more than that unless you play the absolute latest 3D games or edit HD video.

The Hard Drive: Choose the largest drive you can afford. While you won't need all that space in the beginning, you'll want plenty of room for later. Look for a model that has a disk rotation speed of 7200RPM or faster. If your motherboard supports it, consider a serial ATA drive for faster transfers. Look for a large built-in memory cache for better performance. If you're running Windows Vista, you'll want to consider a newer model that contains built in flash RAM for best system operation.

Optical Media Drive: Consider a recordable CD or DVD drive for greatest versatility. As HD-DVD and Blueray drives become more common, these will become a must-have addition.

Graphics Card: For general use, a card with 128MB - 256MB of memory will be fine. For gamers, choose the most powerful card you can afford. If your motherboard supports it, consider a PCI Express card.

Audio Card: Look for a model that has both a line in and a line out in addition to mic and headphone jacks. This will offer the most options for best playback or recording. Some models offer "breakout" boxes that provide connections that can be accessed from the front of the case. Others have external boxes that connect to the internal card via a serial or USB cable. Consider a card capable of 5.1 audio if you wish to edit audio or play games that support multi-channel audio.

Keyboard and Mouse: If you like to relax while you compute, conside wireless models for both. Laser mice will be more accurate than standard optical mice. Stay away from roller ball mice, especially with how cheap optical models have become. Some nice additions to the keyboard include hot buttons for applications, a scroll wheel and multimedia controls. USB for both items will make connecting them easier.

Mounting Hardware: This includes screws to install the motherboard and connect devices. This will usually be provided with the motherboard and devices, but, if not, you'll need to supply your own.